{-# LANGUAGE CPP #-} {-# LANGUAGE TemplateHaskell #-} #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 704 {-# LANGUAGE Trustworthy #-} #endif -- in case we're being loaded from ghci #ifndef MIN_VERSION_template_haskell #define MIN_VERSION_template_haskell(x,y,z) (defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 706) #endif ----------------------------------------------------------------------------- -- | -- Module : Control.Lens.TH -- Copyright : (C) 2012 Edward Kmett, Michael Sloan -- License : BSD-style (see the file LICENSE) -- Maintainer : Edward Kmett -- Stability : experimental -- Portability : TemplateHaskell -- ----------------------------------------------------------------------------- module Control.Lens.TH ( -- * Constructing Lenses Automatically makeLenses, makeLensesFor , makeClassy, makeClassyFor , makeIso -- * Configuring Lenses , makeLensesWith , defaultRules , LensRules(LensRules) , lensRules , classyRules , isoRules , lensIso , lensField , lensClass , lensFlags , LensFlag(..) , simpleLenses , partialLenses , buildTraversals , handleSingletons , singletonIso , singletonRequired , createClass , createInstance , classRequired , singletonAndField , generateSignatures ) where import Control.Applicative import Control.Lens.Fold import Control.Lens.Getter import Control.Lens.Iso import Control.Lens.Setter import Control.Lens.Tuple import Control.Lens.Traversal import Control.Lens.Type import Control.Lens.IndexedLens import Control.Monad import Data.Char (toLower) import Data.Either (lefts) import Data.Foldable hiding (concat) import Data.Function (on) import Data.List as List import Data.Map as Map hiding (toList,map,filter) import Data.Maybe (isNothing,isJust,catMaybes,fromJust) import Data.Ord (comparing) import Data.Set as Set hiding (toList,map,filter) import Data.Set.Lens import Data.Traversable hiding (mapM) import Language.Haskell.TH import Language.Haskell.TH.Lens -- | Flags for lens construction data LensFlag = SimpleLenses | PartialLenses | BuildTraversals | SingletonAndField | SingletonIso | HandleSingletons | SingletonRequired | CreateClass | CreateInstance | ClassRequired | GenerateSignatures deriving (Eq,Ord,Show,Read) -- | Only Generate valid 'Simple' 'Lens' lenses. simpleLenses :: Simple Lens LensRules Bool simpleLenses = lensFlags.contains SimpleLenses -- | Enables the generation of partial lenses, generating runtime errors for -- every constructor that does not have a valid definition for the lens. This -- occurs when the constructor lacks the field, or has multiple fields mapped -- to the same lens. partialLenses :: Simple Lens LensRules Bool partialLenses = lensFlags.contains PartialLenses -- | In the situations that a lens would be partial, when 'partialLenses' is -- used, this flag instead causes traversals to be generated. Only one can be -- used, and if neither are, then compile-time errors are generated. buildTraversals :: Simple Lens LensRules Bool buildTraversals = lensFlags.contains BuildTraversals -- | Handle singleton constructors specially. handleSingletons :: Simple Lens LensRules Bool handleSingletons = lensFlags.contains HandleSingletons -- | When building a singleton 'Iso' (or 'Lens') for a record constructor, build both -- the 'Iso' (or 'Lens') for the record and the one for the field. singletonAndField :: Simple Lens LensRules Bool singletonAndField = lensFlags.contains SingletonAndField -- | Use 'Iso' for singleton constructors. singletonIso :: Simple Lens LensRules Bool singletonIso = lensFlags.contains SingletonIso -- | Expect a single constructor, single field newtype or data type. singletonRequired :: Simple Lens LensRules Bool singletonRequired = lensFlags.contains SingletonRequired -- | Create the class if the constructor is simple and the 'lensClass' rule matches. createClass :: Simple Lens LensRules Bool createClass = lensFlags.contains CreateClass -- | Create the instance if the constructor is simple and the 'lensClass' rule matches. createInstance :: Simple Lens LensRules Bool createInstance = lensFlags.contains CreateInstance -- | Die if the 'lensClass' fails to match. classRequired :: Simple Lens LensRules Bool classRequired = lensFlags.contains ClassRequired -- | Indicate whether or not to supply the signatures for the generated lenses. -- -- Disabling this can be useful if you want to provide a more restricted type signature -- or if you want to supply hand-written haddocks. generateSignatures :: Simple Lens LensRules Bool generateSignatures = lensFlags.contains GenerateSignatures -- | This configuration describes the options we'll be using to make isomorphisms or lenses. data LensRules = LensRules { _lensIso :: String -> Maybe String , _lensField :: String -> Maybe String , _lensClass :: String -> Maybe (String, String) , _lensFlags :: Set LensFlag } -- | Lens to access the convention for naming top level isomorphisms in our lens rules. -- -- Defaults to lowercasing the first letter of the constructor. lensIso :: Simple Lens LensRules (String -> Maybe String) lensIso f (LensRules i n c o) = (\i' -> LensRules i' n c o) <$> f i -- | Lens to access the convention for naming fields in our lens rules. -- -- Defaults to stripping the _ off of the field name, lowercasing the name, and -- rejecting the field if it doesn't start with an '_'. lensField :: Simple Lens LensRules (String -> Maybe String) lensField f (LensRules i n c o) = (\n' -> LensRules i n' c o) <$> f n -- | Retrieve options such as the name of the class and method to put in it to -- build a class around monomorphic data types. lensClass :: Simple Lens LensRules (String -> Maybe (String, String)) lensClass f (LensRules i n c o) = (\c' -> LensRules i n c' o) <$> f c -- | Retrieve options such as the name of the class and method to put in it to -- build a class around monomorphic data types. lensFlags :: Simple Lens LensRules (Set LensFlag) lensFlags f (LensRules i n c o) = LensRules i n c <$> f o -- | Default lens rules defaultRules :: LensRules defaultRules = LensRules top fld (const Nothing) $ Set.fromList [SingletonIso, SingletonAndField, CreateClass, CreateInstance, BuildTraversals, GenerateSignatures] where top (c:cs) = Just (toLower c:cs) top _ = Nothing fld ('_':c:cs) = Just (toLower c:cs) fld _ = Nothing -- | Rules for making fairly simple partial lenses, ignoring the special cases -- for isomorphisms and traversals, and not making any classes. lensRules :: LensRules lensRules = defaultRules & lensIso .~ const Nothing & lensClass .~ const Nothing & handleSingletons .~ True & partialLenses .~ False & buildTraversals .~ True -- | Rules for making lenses and traversals that precompose another lens. classyRules :: LensRules classyRules = defaultRules & lensIso .~ const Nothing & handleSingletons .~ False & lensClass .~ classy & classRequired .~ True & partialLenses .~ False & buildTraversals .~ True where classy :: String -> Maybe (String, String) classy n@(a:as) = Just ("Has" ++ n, toLower a:as) classy _ = Nothing -- | Rules for making an isomorphism from a data type isoRules :: LensRules isoRules = defaultRules & handleSingletons .~ True & singletonRequired .~ True & singletonAndField .~ True -- | Build lenses (and traversals) with a sensible default configuration. -- -- > makeLenses = makeLensesWith lensRules makeLenses :: Name -> Q [Dec] makeLenses = makeLensesWith lensRules -- | Make lenses and traversals for a type, and create a class when the type has no arguments. -- -- /e.g./ -- -- @ -- data Foo = Foo { _fooX, _fooY :: 'Int' } -- 'makeClassy' ''Foo -- @ -- -- will create -- -- @ -- class HasFoo t where -- foo :: 'Simple' 'Lens' t Foo -- instance HasFoo Foo where foo = 'id' -- fooX, fooY :: HasFoo t => 'Simple' 'Lens' t 'Int' -- @ -- -- > makeClassy = makeLensesWith classyRules makeClassy :: Name -> Q [Dec] makeClassy = makeLensesWith classyRules -- | Make a top level isomorphism injecting /into/ the type. -- -- The supplied name is required to be for a type with a single constructor that has a single argument -- -- /e.g./ -- -- @ -- newtype List a = List [a] -- makeIso ''List -- @ -- -- will create -- -- @ -- list :: Iso [a] [b] ('List' a) ('List' b) -- @ -- -- > makeIso = makeLensesWith isoRules makeIso :: Name -> Q [Dec] makeIso = makeLensesWith isoRules -- | Derive lenses and traversals, specifying explicit pairings of @(fieldName, lensName)@. -- -- If you map multiple names to the same label, and it is present in the same constructor then this will generate a 'Traversal'. -- -- /e.g./ -- -- > makeLensesFor [("_foo", "fooLens"), ("baz", "lbaz")] ''Foo -- > makeLensesFor [("_barX", "bar"), ("_barY", "bar)] ''Bar makeLensesFor :: [(String, String)] -> Name -> Q [Dec] makeLensesFor fields = makeLensesWith $ lensRules & lensField .~ (`Prelude.lookup` fields) -- | Derive lenses and traversals, using a named wrapper class, and specifying -- explicit pairings of @(fieldName, traversalName)@. -- -- Example usage: -- -- > makeClassyFor "HasFoo" "foo" [("_foo", "fooLens"), ("bar", "lbar")] ''Foo makeClassyFor :: String -> String -> [(String, String)] -> Name -> Q [Dec] makeClassyFor clsName funName fields = makeLensesWith $ classyRules & lensClass .~ const (Just (clsName,funName)) & lensField .~ (`Prelude.lookup` fields) -- | Build lenses with a custom configuration. makeLensesWith :: LensRules -> Name -> Q [Dec] makeLensesWith cfg nm = do inf <- reify nm case inf of (TyConI decl) -> case deNewtype decl of (DataD ctx tyConName args cons _) -> case cons of [NormalC dataConName [( _,ty)]] | cfg^.handleSingletons -> makeIsoLenses cfg ctx tyConName args dataConName Nothing ty [RecC dataConName [(fld,_,ty)]] | cfg^.handleSingletons -> makeIsoLenses cfg ctx tyConName args dataConName (Just fld) ty _ | cfg^.singletonRequired -> fail "makeLensesWith: A single-constructor single-argument data type is required" | otherwise -> makeFieldLenses cfg ctx tyConName args cons _ -> fail "makeLensesWith: Unsupported data type" _ -> fail "makeLensesWith: Expected the name of a data type or newtype" where deNewtype (NewtypeD ctx tyConName args c d) = DataD ctx tyConName args [c] d deNewtype d = d ----------------------------------------------------------------------------- -- Internal TH Implementation ----------------------------------------------------------------------------- -- | Given a set of names, build a map from those names to a set of fresh names based on them. freshMap :: Set Name -> Q (Map Name Name) freshMap ns = Map.fromList <$> for (toList ns) (\ n -> (,) n <$> newName (nameBase n)) makeIsoTo :: Name -> ExpQ makeIsoTo conName = do f <- newName "f" a <- newName "a" lamE [varP f, conP conName [varP a]] $ appsE [ return (VarE 'fmap) , conE conName , varE f `appE` varE a ] makeIsoFrom :: Name -> ExpQ makeIsoFrom conName = do f <- newName "f" a <- newName "a" b <- newName "b" lamE [varP f, varP a] $ appsE [ return (VarE 'fmap) , lamE [conP conName [varP b]] $ varE b , varE f `appE` (conE conName `appE` varE a) ] makeIsoBody :: Name -> Name -> (Name -> ExpQ) -> (Name -> ExpQ) -> DecQ makeIsoBody lensName conName f g = funD lensName [clause [] (normalB body) []] where body = appsE [ return (VarE 'isomorphic) , f conName , g conName ] makeLensBody :: Name -> Name -> (Name -> ExpQ) -> (Name -> ExpQ) -> DecQ makeLensBody lensName conName f _ = funD lensName [clause [] (normalB (f conName)) []] plain :: TyVarBndr -> TyVarBndr plain (KindedTV t _) = PlainTV t plain (PlainTV t) = PlainTV t appArgs :: Type -> [TyVarBndr] -> Type appArgs t [] = t appArgs t (x:xs) = appArgs (AppT t (VarT (x^.name))) xs apps :: Type -> [Type] -> Type apps = Prelude.foldl AppT appsT :: TypeQ -> [TypeQ] -> TypeQ appsT = Prelude.foldl appT -- | Given -- -- > newtype Cxt b => Foo a b c d = Foo { _baz :: Bar a b } -- -- This will generate: -- -- > foo :: (Cxt b, Cxt f) => Iso (Foo a b c d) (Foo e f g h) (Bar a b) (Bar e f) -- > foo = isomorphic (\f a -> (\(Foo b) -> b) <$> f (Foo a)) -- > (\f (Foo a) -> fmap Foo (f a)) -- > {-# INLINE foo #-} -- > baz :: (Cxt b, Cxt f) => Iso (Bar a b) (Bar e f) (Foo a b c d) (Foo e f g h) -- > baz = isomorphic (\f (Foo a) -> fmap Foo (f a)) -- > (\f a -> fmap (\(Foo b) -> b) (f (Foo a))) -- > {-# INLINE baz #-} makeIsoLenses :: LensRules -> Cxt -> Name -> [TyVarBndr] -> Name -> Maybe Name -> Type -> Q [Dec] makeIsoLenses cfg ctx tyConName tyArgs0 dataConName maybeFieldName partTy = do let tyArgs = map plain tyArgs0 m <- freshMap $ setOf typeVars tyArgs let aty = partTy bty = substTypeVars m aty cty = appArgs (ConT tyConName) tyArgs dty = substTypeVars m cty quantified = ForallT (tyArgs ++ substTypeVars m tyArgs) (ctx ++ substTypeVars m ctx) maybeIsoName = mkName <$> view lensIso cfg (nameBase dataConName) lensOnly = not $ cfg^.singletonIso isoCon | lensOnly = ConT ''Lens | otherwise = ConT ''Iso makeBody | lensOnly = makeLensBody | otherwise = makeIsoBody isoDecls <- flip (maybe (return [])) maybeIsoName $ \isoName -> do let decl = SigD isoName $ quantified $ isoCon `apps` if cfg^.simpleLenses then [aty,aty,cty,cty] else [aty,bty,cty,dty] body <- makeBody isoName dataConName makeIsoFrom makeIsoTo #ifndef INLINING return $ if cfg^.generateSignatures then [decl, body] else [body] #else inlining <- inlinePragma isoName return $ if cfg^.generateSignatures then [decl, body, inlining] else [body, inlining] #endif accessorDecls <- case mkName <$> (maybeFieldName >>= view lensField cfg . nameBase) of jfn@(Just lensName) | (jfn /= maybeIsoName) && (isNothing maybeIsoName || cfg^.singletonAndField) -> do let decl = SigD lensName $ quantified $ isoCon `apps` if cfg^.simpleLenses then [cty,cty,aty,aty] else [cty,dty,aty,bty] body <- makeBody lensName dataConName makeIsoTo makeIsoFrom #ifndef INLINING return $ if cfg^.generateSignatures then [decl, body] else [body] #else inlining <- inlinePragma lensName return $ if cfg^.generateSignatures then [decl, body, inlining] else [body, inlining] #endif _ -> return [] return $ isoDecls ++ accessorDecls makeFieldLensBody :: Bool -> Name -> [(Con, [Name])] -> Maybe Name -> Q Dec makeFieldLensBody isTraversal lensName conList maybeMethodName = case maybeMethodName of Just methodName -> do go <- newName "go" let expr = infixApp (varE methodName) (varE '(Prelude..)) (varE go) funD lensName [ clause [] (normalB expr) [funD go clauses] ] Nothing -> funD lensName clauses where clauses = map buildClause conList buildClause (con, fields) = do f <- newName "_f" vars <- for (con^..conNamedFields._1) $ \fld -> if fld `List.elem` fields then Left <$> ((,) <$> newName ('_':(nameBase fld++"'")) <*> newName ('_':nameBase fld)) else Right <$> newName ('_':nameBase fld) let cpats = map (varP . either fst id) vars -- Deconstruction cvals = map (varE . either snd id) vars -- Reconstruction fpats = map (varP . snd) $ lefts vars -- Lambda patterns fvals = map (appE (varE f) . varE . fst) $ lefts vars -- Functor applications conName = con^.name recon = appsE $ conE conName : cvals expr | not isTraversal && length fields /= 1 = appE (varE 'error) . litE . stringL $ show lensName ++ ": expected a single matching field in " ++ show conName ++ ", found " ++ show (length fields) | List.null fields = appE (varE 'pure) recon | otherwise = let step Nothing r = Just $ infixE (Just $ lamE fpats recon) (varE '(<$>)) (Just r) step (Just l) r = Just $ infixE (Just l) (varE '(<*>)) (Just r) in fromJust $ List.foldl step Nothing fvals -- = infixE (Just $ lamE fpats recon) (varE '(<$>)) $ Just $ List.foldl1 (\l r -> infixE (Just l) (varE '(<*>)) (Just r)) fvals clause [varP f, conP conName cpats] (normalB expr) [] makeFieldLenses :: LensRules -> Cxt -- ^ surrounding cxt driven by the data type context -> Name -- ^ data/newtype constructor name -> [TyVarBndr] -- ^ args -> [Con] -> Q [Dec] makeFieldLenses cfg ctx tyConName tyArgs0 cons = do let tyArgs = map plain tyArgs0 maybeLensClass = do guard $ tyArgs == [] view lensClass cfg $ nameBase tyConName maybeClassName = fmap (^._1.to mkName) maybeLensClass t <- newName "t" a <- newName "a" --TODO: there's probably a more efficient way to do this. lensFields <- map (\xs -> (fst $ head xs, map snd xs)) . groupBy ((==) `on` fst) . sortBy (comparing fst) . concat <$> mapM (getLensFields $ view lensField cfg) cons -- varMultiSet knows how many usages of the type variables there are. let varMultiSet = List.concatMap (toListOf (conFields._2.typeVars)) cons varSet = Set.fromList $ map (view name) tyArgs bodies <- for lensFields $ \(lensName, fields) -> do let fieldTypes = map (view _3) fields -- All of the polymorphic variables not involved in these fields otherVars = varMultiSet List.\\ fieldTypes^..typeVars -- New type variable binders, and the type to represent the selected fields (tyArgs', cty) <- unifyTypes tyArgs fieldTypes -- Map for the polymorphic variables that are only involved in these fields, to new names for them. m <- freshMap . Set.difference varSet $ Set.fromList otherVars let aty | isJust maybeClassName = VarT t | otherwise = appArgs (ConT tyConName) tyArgs' bty = substTypeVars m aty dty = substTypeVars m cty s = setOf folded m relevantBndr b = s^.contains (b^.name) relevantCtx = not . Set.null . Set.intersection s . setOf typeVars tvs = tyArgs' ++ filter relevantBndr (substTypeVars m tyArgs') ps = ctx ++ filter relevantCtx (substTypeVars m ctx) qs = case maybeClassName of Just n | not (cfg^.createClass) -> ClassP n [VarT t] : ps _ -> ps tvs' | isJust maybeClassName && not (cfg^.createClass) = PlainTV t : tvs | otherwise = tvs --TODO: Better way to write this? fieldMap = fromListWith (++) $ map (\(cn,fn,_) -> (cn, [fn])) fields conList = map (\c -> (c, Map.findWithDefault [] (view name c) fieldMap)) cons maybeMethodName = fmap (mkName . view _2) maybeLensClass isTraversal <- do let notSingular = filter ((/= 1) . length . snd) conList showCon (c, fs) = pprint (view name c) ++ " { " ++ concat (intersperse ", " $ map pprint fs) ++ " }" case (cfg^.buildTraversals, cfg^.partialLenses) of (True, True) -> fail "Cannot makeLensesWith both of the flags buildTraversals and partialLenses." (False, True) -> return False (True, False) | List.null notSingular -> return False | otherwise -> return True (False, False) | List.null notSingular -> return False | otherwise -> fail . unlines $ [ "Cannot use 'makeLensesWith' with constructors that don't map just one field" , "to a lens, without using either the buildTraversals or partialLenses flags." , if length conList == 1 then "The following constructor failed this criterion for the " ++ pprint lensName ++ " lens:" else "The following constructors failed this criterion for the " ++ pprint lensName ++ " lens:" ] ++ map showCon conList --TODO: consider detecting simpleLenses, and generating signatures involving "Simple"? let decl = SigD lensName . ForallT tvs' qs . apps (if isTraversal then ConT ''Traversal else ConT ''Lens) $ if cfg^.simpleLenses then [aty,aty,cty,cty] else [aty,bty,cty,dty] body <- makeFieldLensBody isTraversal lensName conList maybeMethodName #ifndef INLINING return $ if cfg^.generateSignatures then [decl, body] else [body] #else inlining <- inlinePragma lensName return $ if cfg^.generateSignatures then [decl, body, inlining] else [body, inlining] #endif let defs = Prelude.concat bodies case maybeLensClass of Nothing -> return defs Just (clsNameString, methodNameString) -> do let clsName = mkName clsNameString methodName = mkName methodNameString Prelude.sequence $ filter (\_ -> cfg^.createClass) [ classD (return []) clsName [PlainTV t] [] ( sigD methodName (appsT (conT ''Lens) [varT t, varT t, conT tyConName, conT tyConName]) : map return defs)] ++ filter (\_ -> cfg^.createInstance) [ instanceD (return []) (conT clsName `appT` conT tyConName) [ funD methodName [clause [varP a] (normalB (varE a)) []] #ifdef INLINING , inlinePragma methodName #endif ]] ++ filter (\_ -> not $ cfg^.createClass) (map return defs) -- | Gets @[(lens name, (constructor name, field name, type))]@ from a record constructor getLensFields :: (String -> Maybe String) -> Con -> Q [(Name, (Name, Name, Type))] getLensFields f (RecC cn fs) = return . catMaybes $ map (\(fn,_,t) -> (\ln -> (mkName ln, (cn,fn,t))) <$> f (nameBase fn)) fs getLensFields _ _ = return [] -- TODO: properly fill this out -- -- Ideally this would unify the different field types, and figure out which polymorphic variables -- need to be the same. For now it just leaves them the same and yields the first type. -- (This leaves us open to inscrutable compile errors in the generated code) unifyTypes :: [TyVarBndr] -> [Type] -> Q ([TyVarBndr], Type) unifyTypes tvs tys = return (tvs, head tys) #if !(MIN_VERSION_template_haskell(2,7,0)) -- | The orphan instance for old versions is bad, but programing without 'Applicative' is worse. instance Applicative Q where pure = return (<*>) = ap #endif #ifdef INLINING inlinePragma :: Name -> Q Dec #if MIN_VERSION_template_haskell(2,8,0) # ifdef OLD_INLINE_PRAGMAS -- 7.6rc1? inlinePragma methodName = pragInlD methodName $ inlineSpecNoPhase Inline False # else -- 7.7.20120830 inlinePragma methodName = pragInlD methodName Inline FunLike AllPhases # endif #else -- GHC <7.6, TH <2.8.0 inlinePragma methodName = pragInlD methodName $ inlineSpecNoPhase True False #endif #endif